Question
I have a willow oak that came up on its own in my back yard by the back fence and is about 4 feet tall now.  It is about 10 feet from my patio and about 20 feet from my slab foundation.  Do willow oaks have shallow or deep roots? I want to avoid buckling of the patio or damage to the foundation.

Answer
This is too close to the house and the roots over time could cause a problem--also the branches will rub on the house. I would transplant it to a better location away from the house.

Deciduous  may be planted either in the spring or the fall. Deciduous plants may be moved in the spring as soon as the frost is out of the ground, up until the time when new foliage is partly unfurled. In the fall, they may be planted once the leaves start to turn color up until the ground freezes.

When you want to dig up a tree or shrub for transplanting, retain as much of the root system as possible.  

Deciduous trees can be successfully moved only if a ball of soil is left around the roots. The exposed roots should be protected with moist burlap or newspaper or with polyethylene sheeting. Every effort should be made to reduce root exposure to wind and sun, keeping the ball as moist as possible. It's best to prepare the hole before digging up the tree you wish to move.

Size of the root ball and size of the hole:

For deciduous trees and shrubs the soil ball should be:

Width = 9-12 in. in diameter/every 1 in. of tree diameter
Depth = 6 in./every 1 in. of tree diameter

For example: A tree trunk 2 inches wide would need a soil ball of 18-24 inches wide and 12 inches deep.

Dig the new hole twice the size of the root ball and as deep and fill with good top soil or potting soil. Mulch around the tree with not more than 3 inches deep of organic mulch not piled up on the trunk.